The invention relates to an electronic circuit arrangement controlling actuators, in particular for controlling the valves and/or the injectors of an injection system of an internal combustion engine.
Conventional injection systems for internal combustion engines for motor vehicles usually have injectors which inject fuel in each case into a combustion space of the internal combustion engine, the injectors being controlled by means of an electronic driver circuit.
Moreover, conventional injection systems have, in addition to the injectors mentioned above, further controllable actuators, for example volume control valves (VCV) or pressure control valves (PCV) which are also controlled by means of an electronic driver circuit. At the input end, the driver circuits are in turn connected to a microcontroller which predefines the desired operating parameters for the actuators, and predefines, for example, the volume flow rate, the fuel pressure and the injection times.
In addition, known injection systems have a monitoring unit which is connected at the output end to a resetting input of the driver circuit in each case, and which can place driver circuits in a predefined safe state when a malfunction occurs. The monitoring unit is connected here to the microcontroller, for example via a databus, in order to be able to detect a malfunction.
In such injection systems, the driver circuits are to be placed in a safe state in all cases when the driver of the motor vehicle switches off the ignition. The microcontroller is therefore connected at the input end to the ignition switch, and when the ignition is switched off said microcontroller controls the monitoring unit in such a way that the driver circuits arc placed in the safe state.
A disadvantage with the known circuit arrangement described above is the fact that both the microcontroller and the monitoring unit must be functioning satisfactorily in order to place the driver circuits in a safe state. If there is a malfunction of the microcontroller or of the monitoring unit there is thus the risk of the driver no longer being able to place the driver circuits in a safe state by switching off the ignition.
The invention is thus based on the object of improving the known circuit arrangement described above to the effect that the driver circuits can be reliably placed in a safe state even if there is a malfunction of the microcontroller or of the monitoring unit.
The object can be achieved by an electronic circuit arrangement for controlling at least one actuator comprising at least one driver circuit with a control input and a resetting input for electrically controlling the actuator as a function of the data which is incoming at the control input, a control unit which is connected at the output end to the resetting input via a resetting line and to the control input of the driver circuit via a control line, and comprising a signal input which is connected internally to the control unit for the external connection of a switching element, the control unit placing the driver circuit in a predefined state when the switching element is activated via the resetting line, wherein the signal input for the switching element is coupled with the resetting input of the driver circuit via a signal path while bypassing the control unit.
A method for checking the resetting of a driver circuit by a control unit in a circuit arrangement, may comprise according to the present invention the following steps:
a resetting input of the driver circuit is activated by means of the control unit via a resetting line,
the behavior of a device which is influenced by an actuator is detected after the activation of the resetting input of the driver circuit,
the behavior of the device which is influenced by the actuator is evaluated in order to check satisfactory resetting of the driver circuit.
The invention comprises the general technical teaching of providing, in addition to the actuation of the resetting input of the driver circuits by the microcontroller or the monitoring unit while bypassing the microcontroller and the monitoring unit, a signal path from the ignition switch to the resetting input of the driver circuits so that the switching off of the driver circuits functions reliably even when there is a malfunction of the microcontroller or of the monitoring unit.
A logic circuit is preferably arranged upstream of the resetting input of the driver circuits and is connected at the input end, on the one hand, to the control unit which is preferably composed of a microcontroller and a monitoring unit, and, on the other hand, to the signal input while bypassing the control unit, for the connection of the ignition switch, the resetting input of the driver circuit being activated if a corresponding activation signal is present at an input of the logic circuit. The resetting of the driver circuit into the safe states therefore take place in this variant of the invention optionally by means of the control unit or directly by means of the ignition switch.
The resetting input of the driver circuit is preferably high active so that the driver circuit is placed in a safe state if a high level is present at the resetting input of the driver circuit. In this case, the logic circuit which is arranged upstream of the resetting input of the driver circuit preferably has an OR gate.
In another variant of the invention, the resetting input of the driver circuit is, on the other hand, low active, so that the driver circuit is placed in a safe state if a low level is present at the resetting input of the driver circuit. In this case, the logic circuit which is connected upstream of the resetting input of the driver circuit preferably has an AND gate.
In one advantageous variant of the invention, a delay element is arranged in the signal path bypassing the control unit, between the signal input for the switching element (for example the ignition switch), which brings about the switching off of the driver circuit, and the resetting input of the driver circuit, the delay of the delay element being preferably longer than the processing time necessary to reset the driver circuits by means of the control unit. This provides the advantage that in the normal operating mode when the control unit is functioning satisfactorily the driver circuits are always reset by means of the control unit and not via the signal path which bypasses the control unit. The delay of the delay element is therefore preferably more than 700 ms, which is generally sufficient.
The control unit for controlling the driver circuits is preferably composed of a microcontroller and a monitoring unit which is connected to the microcontroller, the microcontroller being connected at the output end to the control input of the driver circuit via a control line, whereas the monitoring unit is connected at the output end to the driver circuit via a resetting line. The microcontroller therefore predefines the data (for example fuel pressure, volume flow rate, injection period) with which the driver circuits controls the actuators (for example volume control valve, pressure control valve, injectors), whereas the monitoring unit monitors the operation of the microcontroller and places the driver circuits in a safe state when a malfunction occurs.
In this variant of the invention, the microcontroller and the monitoring unit are preferably connected to one another via a databus, the databus preferably being an SPI (serial peripheral interface) bus.
The variant of the invention described above with a delay element in the signal path which bypasses the control unit provides the advantage that the operational capability of the switching off of the driver circuits by the control unit can be checked in the normal operating mode. In such a monitoring method according to the invention, it is firstly determined whether the ignition switch has been opened, as switching off then takes place in any case after the predefined delay time has expired. The control unit then activates the resetting line for a driver circuit, whereas the resetting lines of the other driver circuit remain uninfluenced. However, when it is functioning satisfactorily the internal combustion engine must nevertheless react with a drop in rotational speed within the delay time as, for example, the volume control valve has been closed. Sensing a corresponding drop in the rotational speed despite the switching off of only a single driver circuit therefore indicates that the associated resetting line is operating satisfactorily.